1. Field of the Invention
The present invention generally relates to image forming apparatuses and carriages and, in particular, to a carriage in which an image forming section is installed and an image forming apparatus having the carriage.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile machine, a copier, and a multi-task machine having plural such functions, there is employed, e.g., a liquid ejection apparatus including a recording head composed of liquid ejection heads (liquid droplet ejection heads) that eject the liquid droplets of recording liquid (liquid) so as to perform image formation. During image formation (used synonymously with recording, printing, and imaging), this liquid ejection apparatus causes liquid (hereinafter referred to as ink) to adhere to a medium, while transferring the medium (hereinafter referred also to as a sheet, but it does not limit the material; also it is used synonymously with a medium to be recorded, a recording medium, a transfer member, a recording paper, etc.).
Note that in the present invention, the “image forming apparatus” refers to an apparatus that ejects liquid onto a medium such as a paper, a thread, a fiber, a fabric, leather, metal, a plastic, glass, wood, and a ceramic so as to perform the image formation. Furthermore, the “image formation” refers to forming on the medium not only meaningful images such as characters and graphics, but also meaningless images such as patterns (i.e., liquid droplets are just ejected and shot). That is, the image forming apparatus refers also to a textile printing apparatus or an apparatus that forms a metal wiring. Furthermore, the “ink” is not particularly limited so long as it is capable of performing the image formation.
When the image forming apparatus of such a liquid droplet ejection type causes a carriage, on which the recording heads that eject liquid droplets are mounted, to reciprocate so as to print the images of ruled lines bi-directionally, the deviation of the ruled lines is likely to occur in forward and backward directions. Furthermore, when printed images in different colors are superposed one on another, slurring is likely to occur.
Generally, in an ink jet recording apparatus or the like, a test chart for adjusting the deviation of shooting positions is output so that users select and input an optimum value. Accordingly, ejection timing is adjusted based on the input results. However, users have their own way of viewing the test chart and are unaccustomed to the operations. Therefore, they are likely to erroneously input data. As a result, an adjustment problem may be adversely incurred.
In view of the above problem, Patent Document 1 describes an image forming apparatus that prints test patterns on a holding and conveying member, such as a conveying belt and a medium, and scans the test patterns with an optical sensor provided in a carriage to correct the deviation of shooting positions.
Patent Document 1: JP-A-2006-264194
Note that examples of image forming apparatuses including an electrophotographic type using the optical sensor are as follows.
Patent Document 2: JP-A-9-226198
Patent Document 3: JP-B2-3397441
Patent Document 4: JP-A-2007-121952
However, when the test patterns formed on the conveying belt are scanned by the optical sensor provided in the carriage, it is difficult to scan the test patterns accurately because their color difference is small depending, for example, on the combination of the color of the conveying belt and that of the ink. In this case, it is necessary to provide a configuration such as a light source whose wavelength is varied for each color so as to detect the colors accurately. In practical sense, however, the test patterns formed on the conveying belt cannot be accurately scanned.
If there is employed, as the conveying belt, an electrostatic one composed of an insulating layer on its front surface and an intermediate resistive layer on its rear surface and incorporating carbon to provide the intermediate resistive layer with a conductive property, the color of the electrostatic belt is black in appearance. Therefore, when the test patterns are detected only by the reflection of the colors, it is difficult to distinguish black ink from the electrostatic belt. As a result, the patterns cannot be detected.
Thus, the present inventor has proposed a method for dealing with the above problem. According to this method, patterns composed of independent ink droplets are formed on the surface of the conveying belt in advance. Then, short-wavelength light is applied to the ink droplets. Taking advantage of the characteristics in which the ink droplets are formed into a semispherical shape, the attenuated amount of regular reflection light is detected according to the formed patterns. As a result, the positions of the patterns and positional deviation can be accurately detected.
Typically, when the conveying surface (called a “detection surface”) of a medium to be recorded, such as the front surface of the medium to be recorded and the conveying belt, is detected using a reflective optical sensor, it turns out that light-receiving sensitivity when the reflective optical sensor is arranged to be slightly inclined is greater than that when the optical sensor applies injection light in a direction perpendicular to the detection surface and receives its reflection light.
On the other hand, the carriage is generally fabricated by injection molding using resin. However, in consideration of the cutting out of the carriage, the injection molding is performed so that a cutting-out direction is perpendicular to the carriage. Therefore, it is necessary to provide a simple structure for mounting and arranging the optical sensor on the side wall surface of the carriage.